This is the text of the window I got when I tried to restore ATV 2G. I have 4.4.3 and when I get to the last step I was unable to put the APT in DFU mode. I gave up and tried to restore it back to basic. I have tried the different solution mentioned by Apple, but in vain. So here I am with a brick. Yes, it’s a beautiful piece of industrial design, but useless nevertheless!
I am new to this myself, but it is important to be in DFU mode. You should be able to restore 4.4.3 version from iTunes without any problem. From my understanding it is very very diffucult to brick aTV, since DFU mode is actually a ROM within a chip that you can’t erase or corrupt, without some “magic”. I found that in some cases it is very difficult to get into DFU mode, not sure why, yet. But instructions are simple, HOLD “Menu” & Play/Pause for ~7 seconds.
Keep trying, try also plugging into a different PC.
Double check that you are in DFU mode by looking at USB Vendor ID and Product ID in Device manager under windows. Product ID should be 1227 and NOT 1281.
If you are running under Windows, then I found ‘ireb’ is a very useful program both to help you get into DFU mode and also tell you when you have succeeded. Can save hours of frustrating iTunes restores going wrong ecause you have not actually succeeded in getting into DFU mode.